Position Tolerancing—Expanded Principles, Symmetry, and Concentricity 9 Position Tolerancing—Expanded Principles, Symmetry, and Concentricity

Specify and explain composite position tolerance specifications. Explain functional gaging methods for checking hole position tolerances specified at MMC. Specify and explain composite position tolerance specifications. Explain the effect of using identical datum feature references in multiple position tolerance specifications. © Goodheart-Willcox Co., Inc.

Specify position tolerances for in-line holes. Specify separate pattern requirements for groups of features not acting as a single pattern. Specify position tolerances for in-line holes. Specify tolerances to control symmetry. Control coaxial features with position or concentricity tolerances, depending on the given application. © Goodheart-Willcox Co., Inc.

Symmetry Position tolerance Symmetry tolerance Symbol removed from standard in 1982 Symbol reinstated in 1994 © Goodheart-Willcox Co., Inc.

Position for Symmetry of Hole Patterns © Goodheart-Willcox Co., Inc.

Symmetry for Features of Size © Goodheart-Willcox Co., Inc.

Concentricity Requires derived median line located relative to datum axis Always has diameter symbol Always applied RFS Must have datum feature reference Datum reference is always RMB Rarely used © Goodheart-Willcox Co., Inc.

Concentricity Feature Control Frame © Goodheart-Willcox Co., Inc.

Concentricity Median Line © Goodheart-Willcox Co., Inc.

Concentricity Zero Error Even though a feature has surface and size variation, it may have no concentricity variation © Goodheart-Willcox Co., Inc.

Composite Position Tolerance One position symbol Two or more segments Same datums, same order, same modifiers © Goodheart-Willcox Co., Inc.

PLTZF Pattern-locating tolerance zone framework Pronounced plotz First segment Located relative to datum reference frame © Goodheart-Willcox Co., Inc.

FRTZF Feature-relating tolerance zone framework Pronounced fritz Lower segment(s) Not located relative to datum reference frame Constrained in rotation relative to referenced datums Must, at a minimum, overlap PLTZF © Goodheart-Willcox Co., Inc.

Composite Position Application © Goodheart-Willcox Co., Inc.

No Repeated Datum References Free to float relative to datum reference frame Features must be able to meet tolerance requirements in first and second segments © Goodheart-Willcox Co., Inc.

Repeated Primary Datum Reference Rotational degrees of freedom constrained relative to primary datum Features must be able to meet tolerance requirements in first and second segments © Goodheart-Willcox Co., Inc.

Repeated Primary and Secondary Datum Reference Rotational degrees of freedom constrained relative to primary and secondary datum Features must be able to meet tolerance requirements in first and second segments © Goodheart-Willcox Co., Inc.

Functional Gaging for Position Tolerances at MMC © Goodheart-Willcox Co., Inc.

Gaging a Composite Position Tolerance Similar to single segment position tolerance Two gages typically required to check composite tolerances © Goodheart-Willcox Co., Inc.

Actual mating envelope A true geometric counterpart of the feature that is at the maximum size that will fit within the hole or other internal feature or at the minimum size that will encompass a shaft or other external feature. Concentricity The allowable position tolerance controlling the derived median line relative to the datum axis.  © Goodheart-Willcox Co., Inc.

Feature-relating tolerance zone framework (FRTZF) The relative true positions of the features in a pattern. Pattern-locating tolerance zone framework (PLTZF) The true positions of the controlled features relative to the referenced datums. © Goodheart-Willcox Co., Inc.

Simultaneous requirement Tolerances shown in the feature control frame that contain identical datum feature references. Symmetry A condition where features on each side of a centerline or center plane are equal. Unrelated actual mating envelope A mating envelope that is not related to any datums and that encompasses all size and form variations on the feature. © Goodheart-Willcox Co., Inc.